1. Field of the Invention
The present invention relates to a lifting engagement chain unit assembled in a lifting apparatus used in a manufacturing facility in the field of various manufacturing industries, in a transport facility in the field of transportation, in a nursing facility in the field of medical and welfare industries, in a stage facility in the field of performing art and the like to lift an object from an installation surface.
2. Related Art
Hitherto, there is known a lifting apparatus for lifting an object which uses a pair of engagement chains which are lifted by rotating a driving sprocket that engages with the engagement chains as disclosed in Japanese Patent Application Laid-open No. Hei. 11-278797. See the claims and FIG. 1. As shown in FIG. 8, the engagement chains used in the lifting apparatus described above lift an object (referred to hereinafter as a ‘driven object’) 220 such as a load supporting member. The driven object 220 is lifted as flat plate end planes 213S, located on the opposite sides from plate engaging planes of link plates 213, contact with each other obliquely with respect to a lifting direction.
One problem with the lifting apparatus described above, however, is that a horizontal component F of a load may be generated as the pair of engagement chains 211 is inclined in lifting the pair of engagement chains 211 by engaging with each other as shown in FIG. 8. Therefore, it becomes difficult to lift the driven object 220 to higher position within a range of a certain chain length by autonomously erecting the pair of engagement chains 211 straightly in a vertical direction. The lifting apparatus also has problems that it may generate a gap between the link plates 213 engaging with each other, may unbalance a burden of the load acting on the respective link plates 213 and may make it difficult to improve buckling strength of the pair of engagement chains 211.
Still more, the inclination of the pair of engagement chains 211 increases even more and the buckling strength also drops in the condition in which the horizontal component F of the load is increased by continuously causing the load to act on the pair of once inclined engagement chains 211 from an upper part to a lower part in the vertical direction. Therefore, the lifting apparatus described above has other problems that it generates a large amount of work to assemble the apparatus because it requires reinforcing devices for reinforcing the pair of engagement chains 211 be mounted. Also, there is a need for an increased number of parts in the apparatus and an increased size of the engagement chains 211, i.e., a cross-sectional area of the pair of engagement chains 211 integrated by engaging with each other, to assure predetermined buckling strength.